High speed process for desizing and bleaching cotton goods



United States Patent HIGH SPEED PROCESS FOR DESIZING AND BLEACHING COTTON GOODS Wilfred Arthur Stephen White, Weston Point, Ru'ncorn, England, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application January 4, 1954, Serial No. 402,132

Claims priority, application Great Britain January? 20, 1953 5 Claims. (Cl. 8139.1)

This invention relates to a process for the treatment of goods containing cotton and more particularly to the preparation of cotton piece goods for dyeing, printing or other finishing treatment for which the cotton is required to be highly absorbent.

As a necessary preliminary to dyeing operations, cotton materials must be prepared so that they do not contain sufiicient colour to interfere with the shade or brightness of the dye and also so that the latter be readily and evenly absorbed by the fabric. In order that the material may be adequately absorbent, it is essential to "remove the greater part of the natural wax present in the cotton as well as the starch which in the case of woven goods has been previously introduced during the warp sizing process. Furthermore, the continuous dyeing processes which are now coming into general use allow only a short time of contact of the cloth with the dye liquor, and hence the cloth must be prepared so as to absorb not only adequately but also rapidly. In addition, a treatment designed to lighten the colour and to remove motes and any non-cellulosic impurities which may spoil the appearance of the finished cloth is desirable. I

Highly absorbent cotton material is also required Where the finishing process is one of impregnation with substances other than dyes as, for example, in the manufacture of typewriter ribbons and waterproof material.

Preparation for dyeing has hitherto been carried out by means of a severe scouring treatment with alkalies; for example woven piece goods often receive an alkaline kier boil and even in many cases a kier boil with alkali followed by a treatment with hypochlorite. It has also been proposed to give the material a preliminary treatment with a volatile organic solvent such as white spirit or a chlorinated hydrocarbon in order to extract the fats and waxes present, but this process was not designed as a substitute for the alkali scour and a subsequent alkaline treatment prior to bleaching was always considered necessary.

The proportion of natural wax present in cotton is only small, but this is removed with difliculty by the alkali treatment; in addition, the latter process is necessarily lengthy and only suitable for batch working, while even when organic solvents are used a complete extraction of the wax takes some hours. Hence while the speed of the dyeing process has increased, the preparative treatment is still long and involved, and it is thus apparent that an effective preparative treatment which could be carried out at a rate comparable with that of the modern dyeing process, and which could be combined with the latter in a continuous operation, would be of considerable value.

It has now been found that the long and severe scouring treatment by kier boiling which was previously thought to be essential for maximum absorbency can be effectively replaced by a very brief treatment with solvent followed by a desizing and part bleaching treatment of comparable length with a peroxygen compound and that,

station not 2,790,699 Patented Apr. 30, 1957 on account of the short time required for these steps, the preparation of the material in a sufficiently absorbent state can be carried out continuously and can be satisfactorily geared to finishing processes of short duration such as the continuous dyeing processes.

According to the invention, therefore, a multi-stage process for the preparation of goods containing cotton for dyeing, printing or other finishing processes requiring a highly absorbent material comprises the steps of continuously and rapidly passing the goods, preferably in open width, through a bath of a hydrocarbon or a chlorinated hydrocarbon solvent where they are degreased and dewaxed and through a bath of an aqueous alkaline solution of a peroxygen compound with which they are desized and bleached.

The two steps may be carried out in any order, but it is generally more convenient to effect the dewaxing treatment first since, like the desizing, the subsequent dyeing operations normally take place in aqueous solution, and if the cloth is wet when it is extracted with the solvent the extraction is impaired. If on the other hand the finishing process is one which also involves an organic solvent, then it may well be more economic to desize first.

Advantageously the solvent is trichlorethylene or perchlorethylene, the peroxygen compound is unneutralised sodium peroxide, and the aqueous solution contains in addition a soluble silicate and also, preferably, a compound having wetting and detergent properties.

Although in the process of the invention the material is only in contact with the solvent for a few minutes at most, the quantity of wax extracted is equivalent to or even more than that obtained by an alkali scour of several hours, the residual wax content of the extracted cotton being from 0.1% to 0.3%. This residual wax can only be removed by several hours extraction with a solvent, but it has been found that its presence does not affect the eventual absorbency of the cotton and it is not deleterious to the dyeing operation. Even complete extraction of the wax does not necessarily render the cotton absorbent and easily wettable, however, and to achieve this the solvent extraction must be followed by a desizing process. For this peroxygen compounds are found to be eminently satisfactory, particularly when used in conjunction with a wetting and detergent agent, in that in addition to giving a high standard of absorbency they also effect partial bleaching and removal of motes. In this part of the process also a contact time of one or two minutes is suflicient to remove from to of the starch present. The resulting material has excellent absorbency.

The complete process is thus eminently suitable for combination with continuous dyeing, and owing to the short contact times in both stages of the process it is practicable to treat the cloth at open width, which gives a better prepare than treatment in rope form. Furthermore the apparatus required is simpler since no devices for long retention are necessary. In comparison with the ordinary alkali scour the process has also the advantages that it produces very little loss in weight of the material, it offers economies in the use of water and there is less harmful effluent, While it also removes adventitious oil stains and renders possible the use of waxy lubricants in warp sizing.

In the dewaxing stage of the process it is preferred to use as solvent a chlorine derivative of methane or ethane. Chloroform, methylene chloride, perchlorethylene and trichlorethylene are all good solvents for the cotton Wax, and of these, trichlorethylene and perchlorethylene are particularly valuable, since in addition to being capable of quickly removing all the easily extractable wax their speed of extraction is very high, even in comparison with other quite useful solvents of the same group. The extraction is improved in both speed and efliciency by the ti l use of hot solvent and by squeezing the cloth at intervals during its passage through the extraction apparatus. The solvent also performs its well known function of degreasing and the material is freed from any adventitious oily matter introduced during processing and any oily matter which may be present in the warp size.

The period of immersion in the solvent need only be from a few seconds up to one minute in duration, and in general extraction times of 15 to 30 seconds are adequate. 30 seconds extraction with hot trichloroethylene, for example, is capable of giving a residual wax content of less than 0.2% on the weight of the cloth. As this operation is to be combined with the desizing process, however, it may be simpler and more convenient to co-ordinate the time of immersion in the solvent with the time required for the second process, which may be longer.

The desizing operation may be effected by immersion of the cloth in the hot solution of the peroxygen compound for a given period, or the cloth may be impregnated with the solution and then steamed for a short time. The latter method is preferable since only a very brief exposure to steam is necessary and the volume of liquid in use can be considerably reduced.

The steaming time of course will vary according to the quantity of peroxide present per litre and to the type of material under treatment but in general 1-2 minutes exposure to steam is adequate for desizing. To increase the degree of bleaching and mote removal eifected by the peroxide solution it may be in certain cases advantageous for the steaming period to be made longer than that necessary for the removal of the size. Also, for the same reasons it may be found advantageous in certain cases to include a retention device after steaming and before washing off so that the material is kept hot for a period while still in contact with the peroxide solution.

Sodium peroxide, sodium percarbonate, sodium perborate and hydrogen peroxide are examples of suitable peroxygen compounds which may be used in the second stage of the process of the invention. The desizing should be carried out in alkaline solution, preferably at a pH of 11 or over, and if the pH of the aqueous solution of the peroxygen compound is not near to this value, then alkali should be added until the desired pH is attained. Sodium peroxide, which gives particularly satisfactory results, is used in aqueous solution in its unneutralized state, such a solution having in the presence of sodium silicate a pH of approximately 11. The product, in addition to being practically free from starch, is also of a good colour which does not yellow back on heating or storage and motes have been largely removed. Owing to the rapidity of the process there is little chance of chemical degradation of the cellulose taking place and the cuprammonium fluidity of the treated material is consistently low. Also, probably again due to the rapidity of the process, materials containing viscose rayon do not appear to have suffered any significant deterioration either due to the oxidising action of the peroxide solution or to the caustic alkali which it contains. In certain cases, however, such as when treating mixtures of cotton with other fibres susceptible to the action of caustic alkalies at elevated temperature, it may be desirable to add also to the sodium peroxide solution an amount of sodium bicarbonate sufiicient to convert part or all of the caustic soda derived from the sodium peroxide into sodium carbonate; this will of course tend to slow down to some extent the desizing operation. The presence of an alkali metal silicate, such as sodium silicate, in the solution is advantageous since this substance acts as a stabiliser and prevents unduly rapid decomposition of the per-compound, and hence improves the colour of the product. It is also desirable to have present a small quantity of a wetting agent which ensures rapid and even wetting and assists in the final rinsing off. The choice of a wetting agent is not of vital importance, but it is preferable to employ a substance which has also a detergent action, since this appears to improve the wettability of the material. The wetting agent should be of neutral or anionic character.

The concentration of the peroxygen compound in the solution will necessarily be dependent upon whether the cloth is to be treated by immersion or whether it is to be impregnated and then steamed. When the former method is used and sodium peroxide is the peroxygen compound, a concentration of as little as 3 grams per litre will give very good results. The steaming process of course requires a stronger solution and it is found that in order to obtain a satisfactory product the concentration of peroxide should be in this case at least 7 grams per litre for a material composed entirely of cotton, While it is preferred to use between 10 and 15 grams per litre. Such a concentration gives a very satisfactory prepare for dyeing when preceded by the first step of solvent extraction. If other per-compounds are to be used, an equivalent concentration calculated on the active oxygen present should be employed.

The quantity of silicate added to the solution is not critical but it should be sutlicient to slow down the decomposition of the per-compound at the high temperatures in use. An amount equivalent to from one-third the weight to an equal weight of the per-compound is usually found to be adequate. Similarly the amount of wetting agent need not be strictly regulated and a generally convenient quantity is about one-twentieth of the weight of the peroxygen compound present.

When the steaming method is used the ratio of weight of solution retained in the cloth to weight of cloth (that is, the liquor ratio) should be preferably between 1.2:1 and 1.7:1. Using this ratio and a solution containing, for example, 10 grams per litre of sodium peroxide, 5 grams per litre of sodium silicate and 0.5 gram per litre of a wetting agent, a satisfactory desizing can be obtained in a minute. It must be understood, however, that in addition to desizing, the function of the peroxygen compound is also to improve the colour of the cloth and to remove motes, and the steaming time must therefore be adequate to take account of all these desired results.

In a preferred form of the process the cloth is passed at open width through one or more enclosed vessels containing a chlorinated hydrocarbon solvent such as trichlorethylene or perchlorethylene maintained at or near to its boiling point. Where there are several vessels the solvent may be allowed to flow from one to the other in the opposite direction to the direction of travel of the cloth, and the rate at which the latter passes through is adjusted according to the contact time desired.

After dewaxing the cloth is freed from solvent; this may be carried out by any known means, for example, by drying with hot air, or by passage through hot water whereby the solvent is flashed off and can be recovered and returned to the dewaxing unit. The second of these methods is particularly advantageous since by its use superior results are obtained during the subsequent desizing operation, probably owing to the very complete wetting with water which the cloth receives in the course of the flashing olf process.

After flashing off, excess water is squeezed from the cloth by means of mangles, and it is passed directly through a bath containing an aqueous solution of unneutralised sodium peroxide which contains also sodium silicate and a wetting and scouring agent. From this the impregnated material passes through a chamber where it is steamed. The cloth is finally rinsed in water, then if desired with dilute acid and again with water. The surplus water is removed and the cloth is then ready for dyeing.

The process of the invention is primarily of use for the treatment of woven piece goods consisting wholly or partially of cotton, but it may also be satisfactorily used for other types of material containing cotton, for instance,

loose fibre stock, yarn or knit goods. Although other natural fibres such as flax contain wax, its presence is usually not objectionable during finishing processes such as dyeing, unlike cotton wax, and although the process of the invention could be used for material other than cotton, there would not appear to be any particular advantage therein.

The following examples illustrate but do not limit the invention:

Example I The same procedure, described hereunder, was carried out both with a cotton drill and with a cotton duck.

Lengths of the fabric which had previously been cropped and singed to remove nebs were passed at open width through two vessels containing trichlorethylene maintained at its boiling point, the total immersion time for each material being 30 seconds. The cloth was then passed through boiling water for 10 seconds in order to flash off the solvent, after which it was padded in an aqueous solution containing 10 grams per litre of sodium peroxide, grams per litre of sodium silicate and 0.5 gram per litre of a wetting and scouring agent consisting of a condensation product of octylated cresol with ethylene oxide. The nip was adjusted so that the cloth retained 1 /2 times its weight of liquor. The impregnated cloth was finally steamed for 1 minute and then rinsed four times in baths containing respectively hot water, cold water, very dilute acetic acid, and cold water. It was then dried, when the wax content of each cloth was found to be 0.31%, while no starch was present, and the wettability was very good.

For comparison, similar cloths were prepared by means of a severe double kier boiling at open width with caustic soda, followed by the customary rinsing with water, scouring and final rinsing with water. After treatment these materials had a wax content of between 0.5% and 0.6% and contained a trace of starch.

Both the materials prepared by the process of the invention and those from the kier boil were subjected to dyeing tests, and the results for the former were superior to those for the kier boiled cloths in respect of colour, value, levelling and penetration.

Example I] Lengths of calico, drill and duck were passed at open width through two baths of boiling trichlorethylene, the immersion time being 30 seconds in each. The solvent was then flashed off by passing the cloth through boiling water for 20 seconds. The solvent-free cloth was desized in the same way as in Example I using the same proportions of peroxide, silicate and wetting agent and the same steaming time. After drying, the wax contents of the three materials were respectively 0.15%, 0.11% and 0.12%, no starch was present, and the wettability was excellent.

Dyeing tests on the prepared cloths gave better results than those for similar cloths which had been prepared by the usual kier boil.

Example 111 A length of grey pillow fabric woven from low grade Indian cotton was passed at open width at a speed of 100 yards per minute through a bath containing trichlorethylene maintained at its boiling point. The cloth passed over a system of rollers in such a way that during its passage through the dewaxing unit it was raised above the solvent five times in all. The total period during which the cloth was in the solvent was 4 /2 seconds.

The solvent remaining in the cloth was removed by drying in air and the cloth was then padded in an aqueous solution containing 15 grams per litre of sodium peroxide, grams per litre of sodium silicate and 0.5 gram per litre of a wetting agent consisting of a condensation product of octylated cresol with ethylene oxide. The nip was adjusted so that the cloth retained approximately 1% was much lighter than the original.

times its weight of liquor. The impregnated cloth was then steamed for 3 minutes in an open width steamer as used in the pad/steam dyeing process. Immediately after leaving the steamer the cloth was rinsed three times with hot water and then in cold water, mangled and dried.

The wax content of the cloth was then found to be 0.25% while no significant amount of starch was present and the wettability was good. In addition the colour of the cloth was much lighter and cotton seed fragments were much less apparent.

The cloth was then subjected to a continuous dyeing test using the leuco method. The dyed cloth was judged to be satisfactory in respect of general appearance, levelness, colour value and degree of penetration.

Example IV A furnishing fabric woven from viscose rayon yarn in the warp direction and grey cotton yarn in the weft was dewaxed by treatment with boiling trichlorethylene for 30 seconds, followed by treatment in boiling water for 20 seconds to remove excess solvent.

The material was then saturated at ordinary temperature with an aqueous solution containing 8 grams per litre of sodium peroxide, 5 grams per litre of sodium silicate and 0.5 gram per litre of a wetting and scouring agent consisting of a condensation product of octylated cresol with ethylene oxide. The excess liquor was removed by a gentle expression so adjusted that the material retained approximately 1.5 times its own weight of liquor. The impregnated cloth was then steamed for 2 minutes and immediately afterwards rinsed with several changes of hot water.

It was found that the material so treated was free from starch and possessed excellent wettability and its colour The material was considered to have been satisfactorily prepared for continuous dyeing The fluidity of a 0.5% solution of the cotton weft yarn in standard cuprammonium wa found to be 2.0 before treatment and 3.1 after treatment, while the fluidity of a 2.0% solution of the rayon warp in standard cuprammonium was found to be 8.7 before treatment and 9.1 after treatment.

Example V The fabric described in Example IV was treated in the same general manner as described in this example, except that the peroxide solution was composed of 10 grams per litre of sodium peroxide, 22 grams per litre of sodium bicarbonate with 5 grams per litre of sodium silicate and 0.5 gram per litre of a wetting and scouring agent consisting of a condensation product of octylated cresol with ethylene oxide. It was found that the material after treatment was substantially free from starch and that its colour and absorbency had been much improved.

What I claim is:

1. A multi-stage process for the preparation of goods containing cotton for dyeing, printing and other finishing processes requiring a highly absorbent material which comprises the steps of continuously passing the goods through a solvent bath selected from the group consisting of trichloroethylene and perchloroethylene where they are degreased and dewaxed, the total necessary immersion time in the bath being not more than three minutes. removing solvent from the goods by contacting them with an aqueous medium held at an elevated temperature sutficient to flash off said solvent, padding the goods in an aqueous alkaline solution of a peroxygen compound and then subjecting the goods to the action of steam for a period requiring not more than three minutes whereby the goods are desized and bleached.

2. The process of claim 1 in which the peroxygen compound is unneutralised sodium peroxide.

3. The process of claim 1 in which the pH of the desizing bath is between 11 and 12.

4. The process of claim 1 wherein said goods are treated in open width.

5. A continuous process for the preparation of goods containing cotton for dyeing, printing and other finishing processes requiring a highly absorbent material which comprises passing the goods through at least one bath of trichlorethylene near its boiling point, the total immersion time being not more than one minute, removing solvent from the goods by contacting them with an aqueous medium held at an elevated temperature sufiicient to flash off said solvent, thereafter padding the goods in an aqueous solution having a pH of 11 to 12 and comprising 10-15 grams per litre of unneutralized sodium peroxide,

together with sodium silicate and a wetting agent, removing excess solution from the goods and adjusting the liquor ratio to between 1.2:1 and 1.7:1 and then subjecting to the action of steam for one to two minutes.

References Cited in the file of this patent UNITED STATES PATENTS 1,020,625 Schewelin Mar. 19, 1912 1,398,378 Jacoby Nov. 29, 1921 1,991,335 Reddish Feb. 12, 1935 2,173,040 Muller Sept. 12, 1939 2,267,718 Campbell Dec. 30, 1941 2,372,561 Elgin Mar. 27, 1945 2,549,014 Romeyn Apr. 17, 1951 

1. A MULTI-STAGE PROCESS FOR THE PREPARATION OF GOODS CONTAINING COTTON FOR DYEING, PRINTING AND OTHER FINISHING PROCESSES REQUIRING A HIGHLY ABSORBENT MATERIAL WHICH COMPRISES THE STEPS OF CONTINUOUSLY PASSING THE GOODS THROUGH A SOLVENT BATH SELECTED FROM THE GROUP CONSISTING OF TRICHLOROETHYLENE AND PERCHLOROETHYLENE WHERE THEY ARE DEGREASED ADN DEWAXED, THE TOTAL NECESSARY IMMERSION TIME IN THE BATH BEING NOT MORE THAN THREE MINUTES, REMOVING SOLVENT FROM THE GOODS BY CONTACTING THEM WITH AN AQUEOUS MEDIUM HELD AT AN ELEVATED TEMPERATURE SUFFICIENT TO FLASH OFF SAID SOLVENT, PADDING THE GOODS IN AN AQUEOUS ALKALINE SOLUTION OF A PEROXYGEN COMPOUND AND THEN SUBJECTING THE GOODS TO THE ACTION OF STEAM FOR A PERIOD REQUIRING NOT MORE THAN THREE MINUTES WHEREBY THE GOODS ARE DESIZES AND BLEACHED 